Beyond the 30-Million-Word Gap: Children's Conversational Exposure Is Associated With Language-Related Brain Function

Abstract

Children's early language exposure impacts their later linguistic skills, cognitive abilities, and academic achievement, and large disparities in language exposure are associated with family socioeconomic status (SES). However, there is little evidence about the neural mechanisms underlying the relation between language experience and linguistic and cognitive development. Here, language experience was measured from home audio recordings of 36 SES-diverse 4- to 6-year-old children. During a story-listening functional MRI task, children who had experienced more conversational turns with adults-independently of SES, IQ, and adult-child utterances alone-exhibited greater left inferior frontal (Broca's area) activation, which significantly explained the relation between children's language exposure and verbal skill. This is the first evidence directly relating children's language environments with neural language processing, specifying both an environmental and a neural mechanism underlying SES disparities in children's language skills. Furthermore, results suggest that conversational experience impacts neural language processing over and above SES or the sheer quantity of words heard.

Keywords: LENA; fMRI; language; open data; open materials; socioeconomic status; turn taking.

Conflict of interest statement

Declaration of Conflicting Interests: <?release-delay 12|0>The author(s) declared that there were no conflicts of interest with respect to the authorship or the publication of this article.

Figures

Fig. 1.

Scatterplots showing composite (a) nonverbal and (b) verbal score as a function of parental education level (mother and father averaged) and household income. Standardized nonverbal assessments evaluated fluid reasoning, nonverbal working memory, and processing speed. Standardized verbal assessments evaluated vocabulary, receptive and expressive morphosyntax, and verbal working memory skill. Dotted lines indicate the average range of scores (within 1 standard deviation of the population mean). Solid lines indicate best-fitting regressions.

Fig. 2.

Scatterplots showing peak hourly (a) adult words and (b) conversational turns as a function of parental education level (mother and father averaged) and household income. Solid lines indicate best-fitting regressions.

Fig. 3.

Scatterplot showing the relationship between children’s composite verbal score (controlled for parental education level and income) and the number of hourly conversational turns. The solid line indicates the best-fitting regression.

Fig. 4.

Regions where activation was significantly greater while listening to forward speech than backward speech, averaged across all participants. Clusters include the whole of the left superior temporal sulcus and the anterior portion of the right superior temporal sulcus.

Fig. 5.

Correlations between activation during language processing and the number of hourly conversational turns children experienced. The brain image in (a) shows the zero-order correlation between the number of conversational turns and activation in the forward > backward speech contrast. Correlations remained significant when controlling for (b) parental education and income, (c) verbal and nonverbal assessment scores, (d) individual numbers of adult words and child utterances, and (e) all of these covariates.

Fig. 6.

Mediation model showing the effect of conversational turns on language assessment scores as mediated by activation in the left inferior frontal gyrus (IFG), shaded in yellow. Activation significantly mediated the relation between the number of conversational turns children experience and their language scores. Solid arrows represent direct paths, whereas the dotted arrow represents the indirect (mediated) path. Asterisks indicate significant paths (*p < .01, **p < .001).